multi threading or QConcurrent for the scenario

[ejoshva]

Hi,

I have a scenario where in I have to show a document on click of the document icon. Each page of the document is a separate html which is encrypted.
Due to the huge number of pages, it take more time to decrypt all the html files and show the page.

Kindly suggest which one is the best suitable (QThread / QConcurrent) , so that I can show the page once the 1st file is decrypted without waiting for all files to complete decrypting process. I want to make the page viewing and the decrypting happen simultaneously once the decrypting of the 1st file is done.

Thanks in advance

[Santosh Reddy]

As you don't need any background activity to be done continuously, it would be better to use QConcurrent, just run the decrypting function QtConcurrent::run().

[ejoshva]

Thanks for the quick response.

[wysota]

I would rather put all pages into a container and use QtConcurrent::map().

[ejoshva]

How do I use QtConcurrent::map()

I have tried to implement QtConcurrent, but it crashes
stating the below error
"Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0 libsystem_kernel.dylib 0x00007fff8cb0f866 __pthread_kill + 10
1 libsystem_pthread.dylib 0x00007fff87aee35c pthread_kill + 92
2 libsystem_c.dylib 0x00007fff89f2fb1a abort + 125
3 org.qt-project.QtCore 0x000000010c1a2159 qt_message_fatal(QtMsgType, QMessageLogContext const&, QString const&) + 9
4 org.qt-project.QtCore 0x000000010c1a3611 QMessageLogger::fatal(char const*, ...) const + 161
5 org.qt-project.QtCore 0x000000010c19e815 qt_assert_x(char const*, char const*, char const*, int) + 85
6 com.yourcompany.learnOn 0x000000010b2cd880 QList<QFileInfo>:perator[](int) + 96 (qlist.h:486)
7 com.yourcompany.learnOn 0x000000010b2cbf8a loadbook::decryptLoop(int, int) + 138 (loadbook.cpp:122)

ASSERT failure in QList<T>:perator[]: "index out of range", file /Applications/QT/5.4/clang_64/lib/QtCore.framework/Headers/qlist.h, line 486
The program has unexpectedly finished.


The code is as below

totalXHtmlPages = 173
    int index=0;
 
    while( index <totalXHtmlPages)
    {
        if(stopThread) return;
 
 
        QFuture<QStringList> test = QtConcurrent::run(this,&loadbook::decryptLoop,index,index+13);
        PgContents.append(test.result());
 
        index = index + 13;
    }
 
 
QStringList loadbook::decryptLoop(int startIndex, int endIndex)
{
    QStringList decryptContent;
    for(int index = startIndex; index < endIndex; index++)
    {
 
        if(stopThread) break;
        decryptContent.append(decrypt->decryptFile(FileInfoList[index].absoluteFilePath(), 'A'));
        qDebug()<<"FileInfoList["<<index<<"] -> "<<FileInfoList[index].absoluteFilePath();
    }
    return decryptContent;
}

totalXHtmlPages = 173
    int index=0;

    while( index <totalXHtmlPages)
    {
        if(stopThread) return;
     

        QFuture<QStringList> test = QtConcurrent::run(this,&loadbook::decryptLoop,index,index+13);
        PgContents.append(test.result());

        index = index + 13;
    }


QStringList loadbook::decryptLoop(int startIndex, int endIndex)
{
    QStringList decryptContent;
    for(int index = startIndex; index < endIndex; index++)
    {

        if(stopThread) break;
        decryptContent.append(decrypt->decryptFile(FileInfoList[index].absoluteFilePath(), 'A'));
        qDebug()<<"FileInfoList["<<index<<"] -> "<<FileInfoList[index].absoluteFilePath();
    }
    return decryptContent;
}

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Here I dont find multiple thread which I intended to create.

how can I make this 173 files to be decrypted as fast as possible using threads

[wysota]

Your code makes no sense. You start a thread only to wait until it finishes executing. Use QtConcurrent::map() as advised.